An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris

Abstract

The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the most extensively studied stars on the AGB. R Scl is a carbon star with a massive circumstellar shell ($M_{shell}\sim 7.3\times 10^{-3}{M}_{\odot }$) which is thought to have been produced during a thermal pulse event $\sim 2200$ years ago. To study the thermal dust emission associated with its circumstellar material, observations were taken with the Faint Object InfraRed CAMera for the SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 $\mu$m. Maps of the infrared emission at these wavelengths were used to study the morphology and temperature structure of the spatially extended dust emission. Using the radiative transfer code DUSTY and fitting the spatial profile of the emission, we find that a geometrically thin dust shell cannot reproduce the observed spatially resolved emission. Instead, a second dust component in addition to the shell is needed to reproduce the observed emission. This component, which lies interior to the dust shell, traces the circumstellar envelope of R Scl. It is best fit by a density profile with $n\propto r^{\alpha }$ where $\alpha =0.75_{-0.25}^{+0.45}$ and dust mass of $M_d=9.0_{-4.1}^{+2.3}\times 10^{-6}{M}_{\odot }$. The strong departure from an $r^{-2}$ law indicates that the mass-loss rate of R Scl has not been constant. This result is consistent with a slow decline in the post-pulse mass-loss which has been inferred from observations of the molecular gas.

10 pages, 10 figures, accepted to ApJ

References in corpus (4)

• Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!
• Near-Infrared Photometry of Carbon Stars
• Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS
• The detached dust shells around the carbon AGB stars R Scl and V644 Sco